Optical brighteners are dyes which are deposited onto fabrics and impart to the fabric an added increment of whiteness/brightness by means of their ability to absorb invisible ultraviolet radiation and re-emit it as visible radiation. Optical brighteners, also known as fluorescent whitener agents, have found widespread use as components of household detergent compositions, including also laundry boosters and fabric softeners.
Sodium hypochlorite is a highly effective bleaching agent and has long been used in conjunction with soaps and detergents to remove stains and other types of soils in the laundering of fabrics. It is generally formulated at a concentration of about 3-8% in water for sale for household use, where it is typically diluted to a concentration of about 200 parts per million (ppm) sodium hypochlorite for laundry bleaching.
To achieve the degree of whiteness desired in the wash by most customers, a combination of bleaching and optical brightening is generally required. This requirement usually is met by using an active fluorescent whitener or fluorescent whitener agent-containing detergent composition as the primary washing agent, combined with a subsequent addition of hypochlorite bleach in a separate step. Thus in order to achieve both bleaching and brightening, a consumer would usually need to use an active, fluorescent whitener agent-containing detergent composition as the primary washing agent, combined with a subsequent addition of hypochlorite bleach to the wash water, or prior to use thereof the addition of a hypochlorite bleach in a separate step. Additionally, the use of a hypochlorite bleach containing fluorescent whitener agents would be advantageous.
Optical brighteners or fluorescent whitener agents are generally insoluble and/or unstable in concentrated hypochlorite, and tend to quickly settle to the bottom of an aqueous hypochlorite solution. In other instances, simple addition of optical brighteners to concentrated aqueous hypochlorite results in a product which must be vigorously shaken each time before use in order to intersperse and mix the ingredients. Because of the tendency for rapid settling, even vigorous shaking before each use does not always result in obtaining a uniform proportion of fluorescent whitener agent and hypochlorite in each use thereof. Further, optical brighteners are known in some instances to be quickly and irreversibly decomposed in the presence of sodium hypochlorite bleach, even at concentrations well below 200 ppm sodium hypochlorite.
It has long been deemed desirable to consolidate bleaching/brightening effects into a single-step process. This could be accomplished by formulating detergents with bleach-stable optical brighteners. Thus in opposition to using subsequent addition of hypochlorite bleach in separate steps with the use of optical brighteners, a detergent which contains an optical brightener which is stable to sodium hypochlorite will still achieve a fabric brightening effect in spite of simultaneous use of the detergent and the sodium hypochlorite.
Another means to consolidate bleaching and brightening into a single-step process is to formulate concentrated (typically about 3-8%) sodium hypochlorite solutions which contain bleach-stable brighteners. Thus both bleaching and brightening can be ensured without regard to the detergent used by the consumer. However, as noted above, optical brighteners are generally unstable in the presence of sodium hypochlorite bleach.
There have been previous attempts to stabilize optical brighteners against reaction with sodium hypochlorite and/or to achieve successful dispersions of optical brighteners in aqueous sodium hypochlorite solutions. For example, U.S. Pat. No. 3,393,153 attempts to present a solution to the problem by including in the composition a particulate material such as colloidal silica or a particulate colloidal polymeric resin which keeps the optical brightener in suspension in aqueous hypochlorite. U.S. Pat. No. 3,393,153 describes an optical brightener/hypochlorite bleach composition, where because of the tendency of rapid settling, even with vigorous shaking before its use, the composition does not necessarily result in obtaining a uniformly proportioned optical brightener and hypochlorite composition.
U.S. Pat. No. 4,526,700 is directed to the formulation of aqueous sodium hypochlorite compositions containing a fine dispersion of a bleach-stable optical brightener. The compositions comprise sodium hypochlorite, the optical brightener 4,4'-bis(4-phenyl-2H-1,2,3-triazol-2-yl)-2,2'-stilbenedisulfonate, certain alkylaryl sulfonate surfactants, and water. The optical brightener is present in the composition in the form of a dispersion of fibrous particles. However, these types of composition's are purportedly stabilized by anionic surfactants, not cationic surfactants. This patent shows a two-phase liquid in which the fluorescent whitener agents are resuspended by shaking before use.
U.S. Pat. No. 4,552,680 is directed to aqueous hypochlorite bleach compositions containing hypochlorite stable surfactants and anti-foaming agents.
U.S. Pat. No. 4,790,953 relates to liquid hypochlorite bleach containing optical brighteners solubilized by amine oxides. These provide a substantially clear and stable aqueous sodium hypochlorite brightener solution.
Many previous attempts to create a stable, practical and useful aqueous bleach product containing both hypochlorite bleach and a fluorescent: whitener agent or optical brightener have failed because of brightener/bleach incompatibility. That is, the efficacy of the optical brightener is destroyed by the bleach and/or some of the oxidizing power of the bleach is reduced by the optical brightener.
In accordance with the present invention, it has been found that anionic optical brighteners (fluorescent whitener agents) or their salts can be made hypochlorite bleach-stable and formula&ed into aqueous sodium hypochlorite solutions or into detergent compositions, in a manner whereby said brightener is transformed into a neutral ion pair with a surface-active quaternary ammonium ion-producing compound. These ion pairs, in which the cationic and anionic portions are in at least relative stoichiometric relationship, form stable aqueous dispersions and remain stable in bleach solutions of varying strengths.